1. Field of the Invention
The present invention is directed to novel urea group-containing polyisocyanates which are modified with long chain compounds having a molecular weight of 400 to about 10,000 and a process for the preparation of these modified polyisocyanates.
2. Description of the Prior Art
Polyisocyanates containing urea groups are known. The diisocyanate prepared from 2 moles of 2,4-toluylene diisocyanate and 1 mole of water has been used in various polyurethane systems (see U.S. Pat. Nos. 4,035,467, 2,818,404, DE 3,230,757 and DE 3,403,498). Also, the urea diisocyanate obtained from 2 moles of 2,6-toluylene diisocyanate and 1 mole of water is known (see U.S. Pat. No. 2,902,474).
These compounds, which are generally in the form of relatively high melting solids, are preferably prepared by reacting the starting polyisocyanates, which are free from urea groups, with water. Various methods are known for conducting this reaction as disclosed in U.S. Pat. Nos. 2,757,184, 3,906,019, DE 3,438,527 and DE 3,638,148).
The urea group-containing polyisocyanates prepared by these processes have in recent times been of great interest as solid isocyanate components for heterogeneous one component systems based on solid polyisocyanates and liquid or solid isocyanate reactive compounds. At low temperatures, the polyisocyanates and isocyanate reactive compounds are present side by side as separate phases in these systems and react very slowly with one another. It is only at relatively high temperatures that these systems become sufficiently compatible with one another to undergo a complete reaction. It is also possible to obtain complete stability in storage of these systems by surface inactivation of the polyisocyanate as disclosed in DE 3,230,757 (EP 103,323) and DE 3,403,500 (EP 150,790).
When polyisocyanates containing urea groups, in particular the produces prepared by the so called "water process" (DE 3,230,757 and DE 3,636,148) are used as the isocyanate component in heterogeneous one component systems which contain relatively low molecular weight isocyanate reactive components, it has been found that the cured end products do not attain the level of properties found in products which have been prepared from the same starting components but by different processes (e.g., by casting a solution obtained by a reaction of the starting components in an appropriate solvent).
This means that the reaction of the components of the heterogeneous system does not proceed quantitatively to form a homogeneous end product. Rather, a portion of the components remains unreacted.
It has now surprisingly been found that this problem may be solved by modifying the urea group containing polyisocyanates with long chain compounds.